
// Utility class to calculate realtime network I/O speed

class SpeedSampler {
    constructor() {
        // milliseconds
        this._firstCheckpoint = 0
        this._lastCheckpoint = 0
        this._intervalBytes = 0
        this._totalBytes = 0
        this._lastSecondBytes = 0

        // compatibility detection
        this._now = Date.now
    }

    reset() {
        this._firstCheckpoint = this._lastCheckpoint = 0
        this._totalBytes = this._intervalBytes = 0
        this._lastSecondBytes = 0
    }

    addBytes(bytes) {
        if (this._firstCheckpoint === 0) {
            this._firstCheckpoint = this._now()
            this._lastCheckpoint = this._firstCheckpoint
            this._intervalBytes += bytes
            this._totalBytes += bytes
        } else if (this._now() - this._lastCheckpoint < 1000) {
            this._intervalBytes += bytes
            this._totalBytes += bytes
        } else { // duration >= 1000
            this._lastSecondBytes = this._intervalBytes
            this._intervalBytes = bytes
            this._totalBytes += bytes
            this._lastCheckpoint = this._now()
        }
    }

    get currentKBps() {
        this.addBytes(0)

        let durationSeconds = (this._now() - this._lastCheckpoint) / 1000
        if (durationSeconds == 0) durationSeconds = 1
            return (this._intervalBytes / durationSeconds) / 1024
    }

    get lastSecondKBps() {
        this.addBytes(0)

        if (this._lastSecondBytes !== 0) {
            return this._lastSecondBytes / 1024
        } else { // lastSecondBytes === 0
            if (this._now() - this._lastCheckpoint >= 500) {
                // if time interval since last checkpoint has exteeded 500ms
                // the speed is nearly accurate
                return this.currentKBps
            } else {
                // we don't know
                return 0
            }
        }
    }

    get averageKBps() {
        let durationSeconds = (this._now() - this._firstCheckpoint) / 1000
        return (this._totalBytes / durationSeconds) / 1024
    }

}

export default SpeedSampler